Memory devices are often used to store information in many products such as computers, digital televisions, digital cameras, cellular phones, and other electronic products. Such memory devices usually have numerous memory cells to store information. In some of these memory devices, the values of information stored in the memory cells can be based on the threshold voltage values of the memory cells. Factors such as changes in operating temperatures and voltages of the memory device may cause the threshold voltage values of the memory cells to change. This may cause the values of the information stored in the memory cells to deviate from their original values. Therefore, the memory device may give incorrect values for the information when the information is retrieved.